In GSM and some other cellular telephone networks, the Home Public Land Mobile Network (HPLMN) of a mobile phone is identified by the Mobile Country Code (MCC) and Mobile Network Code (MNC) pair contained within the International Mobile Subscriber Identity (IMSI) file on the Subscriber Identity Module (SIM) card resident in the mobile phone. For example, the MCC-MNC pair for the Raleigh, N.C. GSM HPLMN is 310-150. Note that the coverage of this HPLMN includes a large geographical area, including Charlotte and Atlanta, among other locations in the southeastern USA.
Due to industry mergers and consolidation, wireless carriers can be a conglomeration of previously disjoint network operators, each having its own HPLMN. A problem arises in that a mobile phone can only have one HPLMN identifier. Yet, a mobile phone can be considered in a home area even when it is outside its HPLMN area. This can occur when the mobile phone is within the coverage area of one of the other network operators that is under the aegis of the wireless carrier.
What is needed is a means for determining if a mobile phone is in a home area without having to rely exclusively on the HPLMN programmed into the mobile phone.